With the advancement in cellular and other wireless communications, there is a significant demand to implement antennas that are “smart” in the sense of being able to tune their operating characteristics (frequency, polarization, radiation pattern, etc) according to the ever-changing wireless communication requirements. Using multiple dedicated antennas to cover a variety of different wireless services that may be scattered over a wide frequency bands increases the system cost, the space requirements for the antennas, and their isolation. Reconfigurable antennas are therefore potential candidates for future RF front-end solutions to minimize the number of antennas required in a particular system.
Reconfigurable antennas have been studied in the wireless communication industry throughout the last two decades or longer. This type of antennas requires some type of reconfiguring element to change the antenna's electrical properties for each channel or communication standard.
Conventional electrically reconfigurable antennas use RF-MEMS, PIN diodes, or varactors to reconfigure their structures and create the required tuning in the antenna function. The activation and de-activation of these switching elements require the incorporation of biasing lines in the radiating plane of the antenna. The switching elements can introduce interference that disturbs the antenna electromagnetic performance. The effects of that interference need to be minimized and the placement of the reconfiguring component needs to be optimized.
The interference effects manifest themselves, first, as unwanted resonances in the operating bands of the antenna. Second the switching interference can cause a change in the antenna radiation pattern away from the design requirements, especially if the biasing lines are not designed properly. To avoid some of these difficulties, and to satisfy the design constraints, reconfigurable antennas can be designed with external matching networks or with reconfiguring elements outside the antenna radiating plane.
On the other hand, some researchers have resorted to optical switches to solve the problems and limitations produced in the electrically reconfigurable antennas. For example, n-type silicon material can be used as a switching element to tune the antenna parameters. One limitation of this technique is the integration of laser diodes within the antenna structure for the switch activation mechanism which adds to the bulkiness of the structure and increases the power consumption of the whole system. Reconfigurable antennas have also been designed using a physical change in the antenna radiating structure. For example, a stepper motor has been proposed to rotate the radiating surface of a microstrip antenna, and for each rotation a different radiating structure is fed. A significant limitation of this technique is the lack of tuning speed.
In addition to reconfigurable antennas, reconfigurable band-pass and band-stop microwave filters have been also investigated as stand-alone components. RF-MEMs, PIN diodes and varactors have been proposed mainly to tune the bandwidth of a filter. However, the non-linearity produced by the switching elements as well as the filter's insertion loss need to be addressed. It may be desirable to provide methods and systems for reconfigurable antennas to, selectively reconfigure their operation without introducing interference, or other issues.